The present invention relates to a power source device, a power supplying method, and portable electronic equipment and an electronic timepiece, employing the power source device, and, particularly, to a technique for efficiently rectifying generated alternating-current power to supply power while controlling a leakage current under no power generation state.
With a generator built in, small portable electronic equipment, such as a wristwatch, is always ready to be operative, requiring no troublesome battery replacement. If the power generated by the generator is an alternating-current power, the use of a diode bridge circuit as a rectifier circuit is contemplated. However, since the diode bridge circuit creates a loss due to a voltage drop through two diodes, the diode bridge circuit is not appropriate for use with the generator for the compact portable electronic equipment, i.e., not appropriate as a rectifier for use with the generator that generates a small-amplitude alternating-current voltage.
To cope with this problem, a rectifier circuit has been proposed which includes a transistor which replaces two of the four diodes in use.
When a voltage level at a first terminal of the generator rises above a threshold voltage of a corresponding first transistor during generation in this arrangement, the first transistor is turned on. A current flows through a closed loop of the first terminalxe2x86x92a first diodexe2x86x92a capacitorxe2x86x92a first transistorxe2x86x92a second terminal. As a result, the capacitor is charged.
On the other hand, when a voltage level at a second terminal of the generator rises above a threshold voltage of a corresponding second transistor, the second transistor is turned on, and a current flows through a closed loop of the second terminalxe2x86x92a second diodexe2x86x92the capacitorxe2x86x92the second transistorxe2x86x92the first terminal. As a result, the capacitor is charged.
The alternating-current voltage generated across the terminals of the generator is full-wave rectified, and the loss due to the voltage drop in full-wave rectification corresponds to the loss through a mere single diode. Even when the generator 0 generates a small-amplitude alternating-current voltage, the charged capacitor or the rectified current is directly able to drive a load.
In practice, the first and second diodes suffer from a leakage current, namely, a minimal current flowing in a no power generation state thereof. When the generator is in the inoperative state thereof, or when the electromotive force thereof is small, the voltage across the terminals of the generator shifts from a common voltage, and the first or second transistor fails to be completely turned off.
The voltage across the terminals of the generator in this state is stabilized to a level, through the leakage current, determined by a voltage division ratio of the resistance component of the diode and the resistance component of the transistor that occurs when the transistor is not completely turned off. The transistor is slightly somewhat in an on state due to the stabilized level. The valuable power stored in the capacitor is charged, and is thus consumed in vain.
Since an extremely low current, as low as several hundred nA, is consumed by the compact portable electronic equipment, the effect of a diode leakage current, as high as several tens of nA, is not negligible.
The present invention has been developed with a view to the above problem, and it is an object of the present invention to provide a power source device, a power supplying method, and portable electronic equipment and an electronic timepiece, for efficiently rectifying a generated alternating-current electromotive force to supply power, while controlling a leakage current to a minimum when the generator is in a no power generation state or when the electromotive force is small in amplitude.
A power source device of the present invention, in a first aspect, for supplying power through a first power line and a second power line, includes a first rectifier unit connected to one terminal to which an alternating-current voltage is supplied, and connected to the first power line, a second rectifier unit connected to the other terminal to which the alternating-current voltage is supplied to, and connected to the first power line, a first switching unit connected between the one terminal and the second power line, a second switching unit connected between the other terminal and the second power line, and a control unit which controls the second switching unit to turn the second switching unit off when no forward current flows through the first rectifier unit, and controls the first switching unit to turn the first switching unit off when no forward current flows through the second rectifier unit.
According to the first aspect of the present invention, the first rectifier unit and the second rectifier unit are respectively diodes.
According to the first aspect of the present invention, a leakage current of the diode, as the first rectifier unit, becomes higher than a leakage current when the first switching unit remains turned off, and a leakage current of the diode, as the second rectifier unit, becomes higher than a leakage current when the second switching unit remains turned off.
According to the first aspect of the present invention, each of the diodes, as the first and second rectifier unit, is respectively integrated in a P-type substrate or an N-type substrate, and the first power line remains higher in potential than the second power line when the diodes are integrated in the N-type substrate, and remains lower in potential than the second power line when the diodes are integrated in the P-type substrate.
According to the first aspect of the present invention each of the first and second switching unit is a field-effect transistor.
According to the first aspect of the present invention, a parasitic diode of the field-effect transistor, as the first switching unit, a parasitic diode of the field-effect transistor, as the second switching unit, the first rectifier unit, and the second rectifier unit form a bridge circuit.
According to the first aspect of the present invention, the control unit includes a first control unit for controlling the second switching unit to turn the second switching unit off when no forward current flows through the first rectifier unit, and a second control unit for controlling the first switching unit to turn the first switching unit off when no forward current flows through the second rectifier unit.
According to the first aspect of the present invention, the control unit compares the voltage level based on the one terminal with the voltage level based on the first power line to determine whether a forward current flows through the first rectifier unit, and compares the voltage level based on the other terminal with the voltage level based on the first power line to determine whether a forward current flows through the second rectifier unit.
According to the first aspect of the present invention, the first power line is higher in potential than the second power line, and the control unit determines whether a forward current flows through the first rectifier unit, based on the determination of whether the voltage level at the one terminal rises above the voltage level that is a sum of a predetermined voltage level and the voltage level of the first power line. The control unit also determines whether a forward current flows through the second rectifier unit, based on the determination of whether the voltage level at the other terminal rises above the voltage level that is a sum of a predetermined voltage level and the voltage level of the first power line.
According to the first aspect of the present invention, the first power line is lower in potential than the second power line, and the control unit determines whether a forward current flows through the first rectifier unit, based on the determination of whether the voltage level at the one terminal is lower in potential than the remainder voltage level that is determined by subtracting a predetermined voltage level from the voltage level of the first power line. The control unit also determines whether a forward current flows through the second rectifier unit, based on the determination of whether the voltage level at the other terminal is lower in potential than the remainder voltage level that is determined by subtracting a predetermined voltage level from the voltage level of the first power line.
According to the first aspect of the present invention, the control unit offsets the predetermined voltage level.
According to the first aspect of the present invention, the predetermined voltage level is equal to a forward voltage of the corresponding rectifier unit.
According to the first aspect of the present invention, at least, the first switching unit, the second switching unit, and the control unit are formed in a single semiconductor substrate.
According to the first aspect of the present invention, a power source device includes a storage unit for storing power supplied through the first power line and the second power line, wherein the storage unit supplies power to the control unit.
According to the first aspect of the present invention, a power source device includes a storage unit for storing power supplied through the first power line and the second power line, wherein the output voltage of the storage unit is stepped up and the power stepped up is supplied to the control unit.
According to the first aspect of the present invention, the first power line is set to a common potential.
According to the first aspect of the present invention, a power source device includes an alternating-current generator unit for generating an alternating-current power to supply the alternating-current power.
A power supplying method of the present invention, in a second aspect, of a power source device for supplying power through a first power line and a second power line, which includes a first rectifier unit connected to one terminal to which an alternating-current voltage is supplied, and connected to the first power line, a second rectifier unit connected to the other terminal to which the alternating-current voltage is supplied to, and connected to the first power line, a first switching unit connected between the one terminal and the second power line, and a second switching unit connected between the other terminal and the second power line, wherein the power supplying method controls the second switching unit to turn the second switching off when no forward current flows through the first rectifier unit, and controls the first switching unit to turn the first switching unit off when no forward current flows through the second rectifier unit.
Portable electronic equipment of the present invention, in a third aspect, includes a generator unit for generating an alternating-current voltage between one terminal and the other terminal thereof, a first rectifier unit connected between the one terminal and a first power line, a second rectifier unit connected between the other terminal and the first power line, a first switching unit connected between the one terminal and the second power line, a second switching unit connected between the other terminal and the second power line, a control unit which controls the second switching unit to turn the second switching off when no forward current flows through the first rectifier unit, and controls the first switching unit to turn the first switching unit off when no forward current flows through the second rectifier unit, and a processing unit, operated from power supplied through the first power line and the second power line, for performing a predetermined processing.
An electronic timepiece of the present invention, in a fourth aspect, includes a generator unit for generating an alternating-current voltage between one terminal and the other terminal thereof, a first rectifier unit connected between the one terminal and a first power line, a second rectifier unit connected between the other terminal and the first power line, a first switching unit connected between the one terminal and the second power line, a second switching unit connected between the other terminal and the second power line, a control unit which controls the second switching unit to turn the second switching off when no forward current flows through the first rectifier unit, and controls the first switching unit to turn the first switching unit off when no forward current flows through the second rectifier unit, and a time measurement unit, operated from power supplied through the first power line and the second power line, for measuring time.